Two. Different. Gods.
The Old Testament God is apparently the Demiurge. The demiurge is given many names in the Gnostic scriptures, but the three most common ones are Yaldabaoth (also spelled “Ialdabaoth”), Samael, and Saklas. “Saklas” comes from the Aramaic word for “fool,” and “Samael” is Aramaic for “Blind God” or “God of the Blind.” The meaning of “Yaldabaoth” is uncertain. The Gnostic text On the Origin of the World fancifully translates it as “Youth, move over there,” but no word or string of words that sounds like “Yaldabaoth” meant that in any ancient Mediterranean language. “Yaldabaoth” is somewhat close to “child of chaos” in Aramaic, but that’s still a stretch, as is the intuitively plausible suggestion that it could be a condensed form of “Yahweh, Lord of Sabbaths.”
The God that Jesus and his Apostles worship is supposed to be the All Father. For the Gnostics, God was nothing like the image of a stern but kind old man in the clouds that, rightly or wrongly, many of us think of when we think of the Christian God. Instead, he was utterly ineffable and inhuman – something that couldn’t be accurately characterized in any human language. You couldn’t even say that he created the world, because that was the work of another, lesser, more human-like being (the demiurge). The Gnostics referred to God as “the One,” “the One Who Is,” “the Great Invisible Spirit,” “the Unknown Silent One,” “the Abyss,”, “the non-being God,” and other such deliberately mysterious designations.
The problem between Old and New testaments is that they are two different Gods. The Jews worship the god of the OT, and The Christians follow the teaching of Jesus and worship the god of the NT. It gets even more substantive when you look into the Synagogue of Satan, or the idea that many “Jews” believe that salvation lie in sin, if that were the case their God should be evil, and the Gnostic scriptures literally say this. Strange as it may at first seem, this, too, was probably a good-faith interpretation of Christian scriptures that were already widespread, popular, and authoritative in the Gnostics’ time. After all, the Gospel of Luke (4:6) and the Gospel of Matthew (4:8) assume that Satan is the ruler of the physical world when Satan offers Jesus the world in exchange for his worship. Likewise, the Gospel of John mentions an evil “ruler (demiurge) of this world” in no less than three places (12:31, 14:30, and 16:11). Luke (10:18) and John (12:31) both speak of Satan or a Satan-like entity ruling the earth from the sky and being vanquished by Jesus’s ministry. 1 John 5:19 is even more blunt: “We know that we are God’s children, and that the whole world lies under the power of the evil one.”